In December 2014 the Turkish government announced that a foreign visitor may enter Turkey with one personal mobile device and use it for up to 60 days via international roaming or with a Turkish SIM cardwithout having to register it.

After 60 days, you must register your device and pay the registration fee or your device will be blocked from the networks.

Registration Requirements

3. Your Turkish residence permit(İkamet Tezkeresi). Military and diplomats on assignment to Turkey, and foreign students studying at Turkish universities, may use certain other forms of Turkish residency identification.

4. Turkish liras to pay the registration fee.

Registration Procedure

Here's how to register your mobile phone:

1. Start the registration process as soon as possible after arriving in Turkey. It must be completed within the first month of your stay in Turkey.

You can also switch on your device and press *#06# on the keypad to reveal your handset's IMEI. Copy the number onto a piece of paper.

3. Take your device, its IMEI, your passport , and your residence permit to a Turkish government tax office (Vergi Dairesi), tell them you have a mobile device imported from abroad (yurt dışından gelen cihazı), and that you want registration (kayıt). You will have to pay TL131.50 for the registration, and you should receive a Vergi Dairesi Alındısı, a paper receipt for payment of the tax, with your mobiel device's IMEI noted on it.

In my case, the officials at the Vergi Dairesi told me it was not possible to register a mobile device with a foreign passport because a Turkish Republic Identity Number (Türkiye Cumhuriyeti Kimlik Numarası) was required, and a foreign national could not have such a number. Turkish friends helped me to discover that it could in fact be done by entering a special number for applicants with non-Turkish passports, 0009151009, authorized by the Office of Information Technologies and Communications Organization (Bilgi Teknolojileri ve İletişim Kurumu, or BTİ, tel. 0 312 294 94 94). The official at the Vergi Dairesi telephoned the BTİ and confirmed that this was true.

This seems straightforward enough (if time-consuming), but registering may be a long,
frustrating
process, and ultimately perhaps unsuccessful. No one seems to know all the requirements of the regulations, or how to fulfill them, so you need a lot of luck to make it work. Read
this...